I've got a weird sound coming from my amp. It sounds like a torn speaker cone, but I've ruled that out because it makes it with different cabs. It's a fizzy sound behind the notes I'm playing and during the notes ringing out. It gets worse with heavy delay and/or overdrive, and with delayed notes on top of each other close together in the scale. I've had this once before, and it was bad solder connections in my pedalboard cables. But now it seems to be doing it when plugged straight into the amp as well. Could it be bad tubes? (It's a Holland amp....EL84 power tubes, but more of a Fendery circuit). Bad solder connections in the amp? Amp not getting enough power? I'm just wondering if anyone has had experience with this. Thanks in advance!!